High-temperature secondary battery based energy storage and power compensation system

ABSTRACT

The high temperature secondary battery based energy storage and power compensation system is so formed that electric power supply system, electric load, and electric energy storage system including a high temperature secondary battery and a power conversion system, are electrically connected with one another. When operating normally, electric power is supplied from the electric power supply system to the electric load, while the electric energy storage system operates to effect peak shaving running and load leveling running. A high speed switch is provided between the electric power supply system and the electric energy storage system, so that when a voltage sag or a service interruption occurs while the electric power is being supplied from the electric power supply system, the voltage sag is immediately detected and the circuit is immediately shut off, an electric power is immediately supplied from the electric energy storage system to the electric load so as to compensate for the voltage sag or the service interruption.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a high-temperature secondarybattery based energy storage and power compensation system.

[0003] 2. Description of the Related Art

[0004] Conventionally, various energy storage systems for carrying out apeak shaving function as well as a load leveling function have beenproposed. Although the proposed systems have been put into practical usein pumped storage hydro, none of the proposed systems has a powercompensation function for compensating for a voltage sag or a serviceinterruption, all of which are likely to happen suddenly in power supplysystems.

[0005] Various electric power quality stabilizing apparatus formed byusing semiconductor electric power conversion apparatuses capable ofinhibiting harmonic distortion as well as voltage fluctuations have alsobeen proposed. In fact, these electric power quality stabilizingapparatuses have been practically used in active filters and static Varcompensator(SVC). Furthermore, to compensate for voltage sag and serviceinterruption, UPSs have been proposed and have already been put intopractical use. However, none of the apparatuses mentioned above has apeak shaving function or a load leveling function.

SUMMARY OF THE INVENTION

[0006] The present invention has been accomplished in order to solve theabove problems, it is an object to provide an economical,high-temperature secondary battery based energy storage and a powercompensation system which has a peak shaving function and a loadleveling function, as well as an electric power quality stabilizingfunction.

[0007] According to the present invention, there is provided ahigh-temperature secondary battery based energy storage and powercompensation system, comprising:

[0008] an electric power supply system;

[0009] an electric load;

[0010] an electric energy storage system including a high-temperaturesecondary battery and a power conversion system (PCS),

[0011] wherein the electric power supply system, the electric load andthe electric energy storage system are electrically connected, and fromwhich, when operating normally, electric power is supplied to theelectric load while the electric energy storage system operates toeffect peak shaving running and load leveling running; and

[0012] a high speed switch provided between the electric power supplysystem and the electric energy storage system;

[0013] when a voltage sag or a service interruption occurs in theelectric power being supplied from the electric power supply system, thevoltage sag is immediately detected, the circuit is temporarily shutoff, electric power is immediately supplied from the electric energystorage system to the electric load in order to compensate for thevoltage sag or the service interruption.

[0014] Further, according to the present invention, the high temperaturesecondary battery is preferably a sodium sulfur battery.

[0015] Moreover, according to the present invention, it is preferredthat the energy storage system for compensating for a voltage sag or aservice interruption is a system capable of outputting a compensationelectric power which is 3 to 8 times the rated electric power of thepeak shaving running and the load leveling running.

[0016] In addition, according to the present invention, it is preferredthat a back-up generator is connected to a circuit on the electric powercompensation side of the high speed switch, a voltage compensationcontroller is provided which is capable of detecting a circuit shut-downeffected by the high speed switch, sending a command in accordance withthe detection signal to cause the energy storage system to discharge aload entire electric power, and at the same time starting the back-upgenerator, so that if the electric power supply is not restored within apredetermined time period, the back-up generator is connected inparallel with the system, while at the same time the electric powersupply from the energy storage system is stopped.

[0017] Furthermore, according to the present invention, it is preferredthat an electric power supply system comprising an electric power supplysystem, an electric load, and an electric energy storage systemincluding a high-temperature secondary battery and a PCS; all of whichbeing electrically connected with one another so as to supply anelectric power from the electric power supply system to the electricload under normal operation conditions, and operating the electricenergy storage system in order to effect peak shaving running and loadleveling running;

[0018] wherein said system further comprises a control function capableof coping with a fluctuation derived from an accident such as a spikeand a frequency fluctuation in the electric power, by detectingimmediately such an accident, and sending a signal based on detection tothe electric energy storage system in order to compensate for thefluctuation.

[0019] Moreover, according to the present invention, it is preferredthat spare high-temperature batteries connected in parallel with themodule batteries are provided so as to cope with a case when the modulebatteries fail, by switching module batteries to the spare batteries.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a schematic view showing one embodiment of the hightemperature secondary battery based energy storage and powercompensation system formed according to the present invention.

[0021]FIG. 2 is a graph showing the contents of the load levelingrunning effected by using the energy storage system of the presentinvention.

[0022]FIG. 3 is a graph showing how a voltage sag when the serviceinterruption occurs in an electric power supply system is prevented byusing the high-temperature secondary battery based energy storage andpower compensation system formed according to the present invention.

[0023]FIG. 4 is a graph showing how a load current having a deformedwave in an electric power supply system is compensated for by using thehigh temperature secondary battery based energy storage and powercompensation system formed according to the present invention.

[0024]FIG. 5 is a schematic view showing an example (1) of anotherembodiment of the high-temperature secondary battery based energystorage and power compensation system formed according to the presentinvention.

[0025]FIG. 6 is a graph showing how an output fluctuation of an electricpower generated by a renewable energy is compensated for, by using thehigh temperature secondary battery based energy storage and powercompensation system formed according to the present invention.

[0026]FIG. 7 is an explanatory view schematically showing an example (2)of another embodiment of the high temperature secondary battery basedenergy storage and power compensation system formed according to thepresent invention.

[0027]FIG. 8 is a graph showing how an output fluctuation of an electricpower sent from a power supply system is compensated for by using thehigh temperature secondary battery based energy storage and powercompensation system formed according to the present invention.

[0028]FIG. 9 is a circuit diagram demonstrating a short-time high-outputfunction of a sodium sulfur battery.

[0029]FIG. 10 is a graph showing a short-time high-output characteristicof the sodium sulfur battery.

[0030]FIG. 11 is an explanatory view showing in detail an example inwhich the high-temperature secondary battery based energy storage andpower compensation system formed according to the present invention isused in an electric load (factory).

[0031]FIG. 12 is an explanatory view showing in detail an example inwhich the high-temperature secondary battery based energy storage andpower compensation system formed according to the present invention andincluding spare batteries are used in an electric load (factory).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The present invention will be explained in detail by referring tothe embodiments described below. However, it is to be understood thatthe invention is not limited to these embodiments.

[0033] At first, the invention will be described in accordance with FIG.1 which represents one embodiment of the present invention.

[0034]FIG. 1 shows a high-temperature secondary battery based energystorage and power compensation system. As shown in the drawing, theenergy storage and power compensation system comprises an electric powersupply system 1, a load 2, and an energy storage system 5, which are allelectrically connected to one another. The energy storage system 5includes a high-temperature secondary battery 3 and a PCS 4. A highspeed switch 6 is provided in the circuit between the electric powersupply system 1 and the electric energy storage system 5. Further, in acircuit formed between the high speed switch 6 and the load 2, a hightemperature secondary battery based energy storage and powercompensation system 8 equipped with a back-up generator 7 is provided. Atransformer 9 is provided on the AC side of the PCS 4, while a circuitbreaker 11 is provided in connection with the back-up generator 7.

[0035] The high-temperature secondary battery based energy storage andpower compensation system 8, which is constructed in accordance with thepresent invention, is usually employed to supply electric power from theelectric power supply system 1 to the load 2. On the other hand, asshown in the graph of FIG. 2, the energy storage system 5 is operated inorder to charge the high temperature secondary battery 3 with electricpower at night, that is during the period from 10 PM to 7 AM. In thisway, it is possible to perform so-called load leveling running in whichthe stored electricity can be discharged during the day time when arelatively large amount of electricity is required, as well as so-calledpeak shaving running in which the stored electricity can be dischargedduring the period from 1 PM to 3 PM in summer when a relatively largeamount of electricity is required.

[0036] In FIG. 2, the broken line shows the load curve of during oneday, and the solid line shows the electric power supply from the gridduring one day. During the period of 10 PM to 7 AM, some of the electricpower in the night is used to charge a sodium sulfur battery 3 in theelectric energy storage system 5. Conversely, during the period from 8AM to 6 PM, an amount of the stored electricity is discharged from theelectric energy storage system 5 in order to meet the demandscorresponding to the increased electric load during this period of time,thereby the reduction in a maximum amount of electric power in theelectric power supply system can be attained.

[0037] In the case where a sodium sulfur battery is used as ahigh-temperature secondary battery, the sodium sulfur battery not onlyhas a high density and a long usable lifetime, but also can produce ahigh output within a short time period and has a high speed response.Furthermore, the electric energy storage system using the sodium sulfurbattery can be fully automated. Moreover, since the electric energystorage system 5 is completely sealed, maintenance is easy. In this way,the electric energy storage and power compensation system 8 according tothe present invention is characterized in that it uses a sodium sulfurbattery. However, such a high-temperature secondary battery may also bea sodium·metal chloride battery.

[0038] Usually, whenever a voltage sag occurs in the electric powerbeing supplied from the electric power supply system 1 or a serviceinterruption occurs, such an accident affects adversely on the electricload 2. In particular, when the electric load 2 is an importantproduction equipment controlled by computer, such a momentary voltagedrop can cause a considerably severe damage to the production system.

[0039] In order to properly deal with a situation in which a voltage sagor a service interruption occurs, a back-up generator is usuallyprovided in an electric power supply circuit. However, a problem stillexists that at least 10 seconds are required for the back-up generatorto start supplying the necessary electric power to the electric load.

[0040] The high temperature secondary battery based energy storage andpower compensation system 8 according to the present invention is formedso that it can operate in the manner shown in FIG. 3. Namely, wheneverthere is a voltage sag in the electric power being supplied from theelectric power supply system 1 or a service interruption occurs, thehigh speed switch 6 will operate to immediately shut off the circuit,while at the same time effecting a temporary, instantaneous discharge ofthe entire electric load from the electric energy storage system 5.Meanwhile, the generator is started, and there is an interval of aboutfifteen seconds, before the entire load electric power is shifted to thegenerator. In fact, the interval of about fifteen seconds can becompensated for by an electric power output from the electric energystorage system 5 utilizing the sodium sulfur battery.

[0041] As shown in FIG. 3, the high speed switch 6 operates at time t₁to shut off the circuit, and the electric energy storage system 5utilizing the sodium sulfur battery will immediately start to supply anelectric power, and at the same time, the generator is started. Then,about fifteen seconds later, i.e., at t₂, the generator 7 is fullycompletely started and the circuit breaker is operated. Afterwards, att₃, the shift from the sodium sulfur battery to the generator iscompletely, thereby ending the electric discharge from the electricenergy storage system 5.

[0042] On the other hand, in the case where a power compensation isneeded only for a voltage sag, it is not necessary to use the back-upgenerator 7. A semiconductor switch is preferably used as the high speedshut-off switch 6. This is because, whenever there is a voltage sag, thesemiconductor switch can immediately shut off the circuit and thusexhibits an excellent high speed response. If the circuit does not shutoff immediately, the electric power discharged from the energy storagesystem 5 utilizing a sodium sulfur battery having an excellent highspeed response will undesirably flow back to the power supply system,rending it impossible to supply electric power corresponding to a loadelectric power to be compensated to the load.

[0043] Furthermore, it is possible to make use of the sodium sulfurbattery system having a PCS. Namely, as shown in FIG. 4, the loadcurrent having a deformed wave can be improved to an overall loadcurrent without any distortion by virtue of a distortion compensationoutput from the energy storage system 5 utilizing the sodium sulfurbattery.

[0044] As described in the above, the energy storage and powercompensation system 8 according to the present invention can, undernormal operation, perform load leveling running as well as peak shavingrunning. Meanwhile, the energy storage and power compensation system caninstantly compensate for an entire electric load whenever there is avoltage sag or when a service interruption occurs, thereby protectingimportant load or manufacturing system from severe damage. In addition,it is also possible to stabilize the quality of an electric power ateach terminal of the system, as well as to effect an SVC running.

[0045]FIG. 5 is used to indicate one example (1) serving as anotherembodiment for carrying out the present invention.

[0046] When electricity generating equipment 13 using renewable energyis provided in an electric power supply system located between adistribution substation 12 and an electric power user 2, the energystorage and power compensation system 8 formed according to the presentinvention can be operated to compensate for an output fluctuation of thegenerator 13.

[0047] That is, this embodiment is directed to an energy storage andpower compensation system comprising an electric power supply system 1,and an electric energy storage system 5 being is connected with saidsupply system and consisting of a sodium sulfur battery 3 and a PCS 4,characterized in that an electric power compensation controller 14capable of detecting an output from the generator 13 and outputting asignal to supply an electric power from the energy storage system 5 forcompensating the output is provided between the electricity generatingequipment 13 and the electric energy storage system 5.

[0048] Thus, the electric energy storage system 5 is capable of not onlyperforming a load leveling running and a peak shaving running, but alsoabsorbing output fluctuation derived from a variation in nature of theelectricity generating equipment 13 involving the use of renewableenergy resource.

[0049]FIG. 6 shows an example wherein an output fluctuation of theelectricity generating equipment 13 equipped with a solar cell and awind turbine generator was compensated by outputting a power from theenergy storage system 5 based on the electric power compensationcontroller 14 so as to cope with the fluctuation during the period offrom 8 AM to 6 PM.

[0050]FIG. 7 shows an example (2) serving as a further embodiment forcarrying out the present invention.

[0051] The energy storage and power compensation system 8 according tothis embodiment of the present invention comprising an electric energystorage system 5 consisting of a sodium sulfur battery 3 and a PCS 4being provided in a power supply system 1 extending between thedistribution substation 12 and the electric load 2; characterized inthat an electric power quality stabilizing controller 15 capable ofdetecting the voltage, the current and the frequency of an electricpower supplied from the power supply system 1, and also capable ofoutputting power in proportion to deflections of the above parametersfrom the energy storage system 5, in accordance with detection signals,is provided between the electric power supply system 1 and the electricenergy storage system 5.

[0052] Thus, the electric energy storage system 5 is capable ofperforming not only load leveling running and peak shaving running, butalso operations in proportion to the electric power fluctuation.Therefore, it is possible to effect a desired compensation to ensurestabilized power supply.

[0053]FIG. 8 shows an example in which the controller operates to obtaina compensation electric power from the energy storage system 5, so as tocompensate for various fluctuations of an electric power flowing to theelectric power system 1, thereby ensuring a high quality electric powersupply.

Examples

[0054] Examples of the present invention will be described in thefollowing.

Example 1

[0055] This example shows a short-time high-output function of thesodium sulfur battery.

[0056] A sodium sulfur single battery (open-circuit voltage 2.075 V), a28-mΩ resistor 17 a, a 1-mΩ resistor 17 b, and a switch 18 are connectedin the manner shown in FIG. 9, thereby forming a predetermined circuit.A rated discharge is performed on the 28-mΩ resistor 17 a, the switch 18is opened or closed so as to effect a short-time high-output dischargeon the 1-mΩ resistor 17 b. FIG. 10 (which is a graph) shows the resultobtained when a high output discharge is repeated every hour during therated discharge.

[0057] As shown in the graph, during 15 second-output and 30second-output, it is possible to effect a discharge which is about 5 to6 times greater than a rated current (for eight hours). Namely, thesodium sulfur battery based energy storage and power compensation systemformed according to the present invention is characterized in that itemploys the above described sodium sulfur battery, forming a systemcapable of performing a load leveling running, as well as providing afunction of preventing an instantaneous voltage drop.

Example 2

[0058]FIG. 11 shows in detail an example in which the sodium sulfurbattery based energy storage and power compensation system 8 formedaccording to the present invention can be used in an electric load(factory) 2 having a total load of 5 MW.

[0059] A energy storage system 5 including ten units of 500 KW PCSs 4and sodium sulfur batteries 3 is electrically connected to a high speedsemiconductor switch 6, an electric power supply system 1 and anelectric load 2, in the manner shown in FIG. 11. Under normal operation,the energy storage system 5 receives at night an electric charge fromthe electric power supply system 1, but during daytime when there areincreased needs for electric power because a lot of electric load suchas air conditioning equipment and air conditioners are in use, theenergy storage system 5 discharges 1 MW electric power, therebyeffecting load leveling running.

[0060] When there is a voltage sag or a service interruption, the highspeed switch 6 operates to immediately shut off the circuit, while atthe same time an electric power of 5 MW is spontaneously discharged fromthe energy storage system 5 within 30 seconds, thereby ensuring a powersupply having stabilized quality without any voltage drop, until theservice interruption is over and an ordinary power supply has beenrestored.

[0061] In FIG. 11, the discharge is indicated as a PQ discharge (PowerQuality discharge). In the case there is a back-up generator (notshown), 30 seconds would be sufficient to bridge the power source fromthe energy storage system to the back-up generator. Accordingly, even ifthe service interruption period is relatively long, it is still possibleto supply an electric power having a high and stabilized quality to theelectric load (factory) 2.

[0062]FIG. 12 shows in detail an example in which a group of sparebatteries 19 are arranged for use with a high-temperature battery systemof the present invention, which is provided for an electric load havinga total load of 10 MW. If, in the event of an accident, a module battery3 has a failure, the failed group is opened while the spare group 19 canbe connected in parallel to the circuit, thereby improving thereliability for supplying an electric power. In such a case, since eachgroup includes 2 module batteries 3, if the system is used for a longtime, the second battery also fails, a healthy module battery of thefailed group (in opened condition) can be used to replace the secondfailed battery. In this way, it is possible for the system to run for anextremely long time, ensuring an improved reliability.

[0063] As may be understood from the above description, thehigh-temperature secondary battery based energy storage and powercompensation system formed according to the present invention, is asystem capable of performing peak shaving running as well as loadleveling running, thereby ensuring an improved, stable, and high qualityelectric power supply. Therefore, the energy storage and powercompensation system of the present invention is suitable not only foreffectively making use of the electric power in the night time, but isalso suitable for supplying to a factory or the like facilities a highquality electric power capable of preventing an voltage sag in importantequipment, stabilizing an output electric power generated even byfluctuating renewable energy, and which is capable of compensating forspike, frequency fluctuations and harmonic distortions.

What is claimed is:
 1. A high-temperature secondary battery based energystorage and power compensation system, comprising: an electric powersupply system; an electric load ; an electric energy storage systemincluding a high-temperature secondary battery and a power conversionsystem, wherein the electric power supply system, the electric load andthe electric energy storage system are electrically connected, and fromwhich, when operating normally, electric power is supplied to theelectric load while the electric energy storage system operates toeffect peak shaving running and load leveling running; and a high speedswitch provided between the electric power supply system and theelectric energy storage system; when a voltage sag or a serviceinterruption occurs in the electric power being supplied from theelectric power supply system, the voltage sag is immediately detected,circuit is temporarily shut off, electric power is immediately suppliedfrom the electric energy storage system to the electric load in order tocompensate for the voltage sag or the service interruption.
 2. Ahigh-temperature secondary battery based energy storage and powercompensation system according to claim 1 , wherein the high-temperaturesecondary battery is a sodium sulfur battery.
 3. A high-temperaturesecondary battery based energy storage and power compensation systemaccording to claim 1 , wherein the energy storage system forcompensating for the voltage sag or the service interruption is a systemcapable of outputting a compensation electric power which is 3 to 8times a rated electric power of the peak shaving running and the loadleveling running.
 4. A high-temperature secondary battery based energystorage and power compensation system according to claim 1 , furthercomprising: a back-up generator which is connected to the circuit on theelectric power compensation side of the high speed switch; a voltagecompensation controller capable of detecting a circuit shut-off effectedby the high speed switch, sending a command in accordance with adetection signal to cause the energy storage system to discharge anentire electric load, and, at the same time, starting the back-upgenerator, so that if the electric power supply is not restored within apredetermined time period, the back-up generator is connected inparallel with the system, while at the same time the electric powersupply from the energy storage system is stopped.
 5. A high-temperaturesecondary battery based energy storage and power compensation systemcomprising the electric power supply system, the electric load, and theelectric energy storage system including the high-temperature secondarybattery and the power conversion system; all of which being electricallyconnected with one another so as to supply an electric power from theelectric power supply system to the electric load under normal operationconditions, and operating the electric energy storage system in order toeffect peak shaving running and load leveling running according to claim1 , wherein said system further comprises a control function capable ofcoping with a fluctuation derived from an event such as a spike and afrequency fluctuation in the electric power supplied, by detectingimmediately such an event, and sending a signal based on detection tothe electric energy storage system in order to compensate for thefluctuation.
 6. A high-temperature secondary battery based energystorage and power compensation system according to claim 1 , whereinspare high temperature batteries connected in parallel with module hightemperature batteries are provided so as to cope with a case that modulebatteries fail by switching from failed module batteries to the sparehigh temperature batteries.